The sql connection object
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The document discusses the SqlConnection and SqlCommand objects in .NET for interacting with a SQL database. The SqlConnection represents a connection to a database and must be instantiated before performing any operations. The SqlCommand allows specifying query and non-query commands to perform operations like selecting, inserting, updating, and deleting data. Methods like ExecuteReader, ExecuteNonQuery, and ExecuteScalar are used to execute queries and commands.
The sql connection object
- 2. • The first thing you will need to do when interacting with a data base is to create a connection.
- 3. Creating a SqlConnection Object • A SqlConnection is an object, • SqlConnection conn = new SqlConnection( "Data Source=(local);Initial Catalog=Northwind;Integrated Security=SSPI"); • SqlConnection conn = new SqlConnection( "Data Source=DatabaseServer;Initial Catalog=Northwind;User ID=YourUserID;Password=YourPassword");
- 4. Using a SqlConnection • Instantiate the SqlConnection. • Open the connection. • Pass the connection to other ADO.NET objects. • Perform database operations with the other ADO.NET objects. • Close the connection.
- 5. The SqlCommand Object • A SqlCommand object allows you to specify what type of interaction you want to perform with a database. • SqlCommand cmd = new SqlCommand("select CategoryName from Categories", conn);
- 6. • // 1. Instantiate a new command with a query and connection SqlCommand cmd = new SqlCommand("select CategoryName from Categories", conn); // 2. Call Execute reader to get query results SqlDataReader rdr = cmd.ExecuteReader();
- 7. Inserting Data • To insert data into a database, use the ExecuteNonQuery method of the SqlCommand object.
- 8. // prepare command string • string insertString = @" insert into Categories (CategoryName, Description) values ('Miscellaneous', 'Whatever doesn''t fit elsewhere')"
- 9. • // 1. Instantiate a new command with a query and connection SqlCommand cmd = new SqlCommand(insertString, conn); // 2. Call ExecuteNonQuery to send command cmd.ExecuteNonQuery();
- 10. Updating Data • // prepare command string string updateString = @" update Categories set CategoryName = 'Other' where CategoryName = 'Miscellaneous'";
- 11. • // 1. Instantiate a new command with command text only SqlCommand cmd = new SqlCommand(updateString); // 2. Set the Connection property cmd.Connection = conn; // 3. Call ExecuteNonQuery to send command cmd.ExecuteNonQuery();
- 12. Deleting Data • // prepare command string string deleteString = @" delete from Categories where CategoryName = 'Other'";
- 13. • // 1. Instantiate a new command SqlCommand cmd = new SqlCommand(); // 2. Set the CommandText property cmd.CommandText = deleteString; // 3. Set the Connection property cmd.Connection = conn; // 4. Call ExecuteNonQuery to send command cmd.ExecuteNonQuery();
- 14. Getting Single values • Sometimes all you need from a database is a single value, which could be a count, sum, average, or other aggregated value from a data set.
- 15. • // 1. Instantiate a new command SqlCommand cmd = new SqlCommand("select count(*) from Categories", conn); // 2. Call ExecuteNonQuery to send command int count = (int)cmd.ExecuteScalar();